A defence lawyer at a landmark Canadian trial stemming from the Rwandan genocide questioned Romeo Dallaire's memory Wednesday, suggesting the trauma of the bloodbath might have made it tough for the former general to remember details.

Dallaire, the former head of the doomed United Nations peacekeeping mission in Rwanda, has testified for two days at the war crimes trial of Désiré Munyaneza.

Defence lawyer Laurence Cohen asked Dallaire if the trauma of his time spent amid the massacre of some 800,000 Rwandans might affect his memory.

"On the contrary," Dallaire said in the witness box at Quebec Superior Court in Montreal.

"Post-traumatic stress disorder hard-wires events in your brain to the extent they will come back in digitally clear detail to your brain.

"You don't actually remember them. You relive them."

Dallaire was discharged from the military for PTSD a few years after the 1994 mission, where his force tried in vain to stop the slaughter of more than 800,000 Tutsis and moderate Hutus.

He attempted suicide several times before learning to cope thanks to medication and therapy.

Munyaneza, who used to live in Toronto, is accused of being a Hutu militia leader who headed a rampage of rape and murder in the Butare region of Rwanda in 1994.

The 40-year-old, charged with genocide, is the first to be tried under Canada's Crimes Against Humanity and War Crimes Act, enacted in 2000.

Munyaneza was arrested at his Toronto home in 2005 after a six-year RCMP investigation.

Dallaire describes climate of mistrust during mission

The prosecution called Dallaire as a witness to contextualize the Rwandan genocide, which took place over a 100-day period in 1994.

Under defence questioning, Dallaire admitted he was a neophyte at international field command when he took on the UN mission in 1993, despite more than 30 years in the army.

He also said Rwanda's Hutu-led government questioned the impartiality of his UN mission, saying he was sympathetic to the Tutsi minority and its rebel army.

In April 1994, seven months after Dallaire's mission began, Hutu-backed militias led the massacre of Tutsis and Hutu moderates.

Dallaire recalled how people perpetrating massacres, mainly by machete, seemed detached from the slaughter.

"It became completely depersonalized," he said. "It was like cutting fruit for them."

Dallaire also described how most developed nations refused to contribute troops to the mission from the outset and when the massacres began.

Western countries that did contribute significant numbers tended to be former colonial masters in Africa that were there for their own interests.

Shortly after the massacres began, several hundred Belgian troops left because 10 of their soldiers were killed.

Later, the French sent troops who mainly seemed concerned with allowing Hutu and militia leaders to escape the advancing Tutsi rebel army, Dallaire said.

With files from the Canadian Press